1. Field of the Invention
This invention relates to an interlock circuit for a working vehicle having a vehicle body, a working implement attached to the vehicle body, a clutch mechanism switchable between an engaged state for transmitting power to the working implement and a disengaged state for breaking power transmission to the working implement, and a shifting device for determining a traveling direction of the vehicle body. More particularly, the invention relates to an interlock circuit having a check function to check a backward operational run in which the vehicle body travels backward with the clutch mechanism engaged, and a release function to permit a backward operational run by canceling the check function.
2. Description of the Related Art
An interlock circuit for a working vehicle having the above construction is shown in U.S. Pat. No. 5,994,857, for example. This prior art construction, basically, checks a PTO (power takeoff) operation when the vehicle travels backward. Particularly when, with the PTO operated, a switch is moved to a momentary on position before the vehicle travels backward, the vehicle is allowed to travel backward (release state). Even when the switch is moved from the momentary on position, the PTO operation is continued as long as the vehicle travels backward. The release state is canceled to stop the PTO operation when the PTO is turned off or the vehicle is reversed to travel forward.
In the above prior art construction, the vehicle is allowed to travel backward with the PTO operated only when the vehicle is caused to travel backward by consciously operating switches in a state of operating the PTO. A backward run with the PTO operated is prevented when the operator makes an operational error or fails to pay good attention, to call for a careful operation. Take an operation with a mower unit for example. When cutting grass around trees or adjacent a fence having a complicated shape, the grass may be cut efficiently by reversing the vehicle back and forth repeatedly with the mower unit operated. In carrying out an operation in such a mode, the mower unit needs to be operated continuously. With the above prior construction, a switch must be operated before driving the vehicle backward, and besides, the PTO operation is stopped when the vehicle is driven forward. Where an operation is performed by driving the vehicle back and forth repeatedly, the switch must be operated each time the vehicle is placed in reverse, which is troublesome. From this viewpoint, the above prior construction has room for improvement.
The object of this invention is to provide an interlock circuit for a working vehicle, which allows an operation to be carried out by backing the vehicle as necessary, without imposing a troublesome task on the operator.
The above object is fulfilled, according to this invention, by an interlock circuit comprising a check function circuit for performing a check function, the check function circuit being formed of a circuit portion for checking a backward operational run based on a signal indicating a state of the clutch mechanism and a signal indicating a traveling direction of the vehicle body determined by the shifting device; and a release function circuit for performing a release function, the a release function circuit being formed of a circuit portion having a release switch operable to cancel the check function continuously when the signal indicating a state of the clutch mechanism indicates that the clutch mechanism is engaged, and the signal indicating a traveling direction of the vehicle body indicates forward or neutral.
With this construction, when the operator attempts a backward operation run by driving the vehicle body backward with the clutch mechanism engaged, the check function circuit checks the backward operational run based on the signal indicating the state of the clutch mechanism and the signal indicating the traveling direction of the vehicle body. The check function of the check function circuit is canceled only by operating the release switch with the clutch mechanism engaged, and the traveling direction of the vehicle body set to forward or neutral. When the check function of the check function circuit is canceled as above, the check function remains off. Thus, the working implement may be driven continuously when an operation is carried out by reversing the vehicle body backward and forward repeatedly. It is no longer necessary to operate the switch prior to each backward operational run as in the prior art. That is, the interlock circuit according to this invention allows a backward operational run to be performed easily and simply by operating the release switch.
In one preferred embodiment of this invention, the release function circuit is constructed to cancel the release function in favor of the check function when the clutch mechanism is disengaged while the release function is in operation. With this construction, the check function of the check function circuit is reinstated by disengaging the clutch mechanism while the check function is continuously released. Thereafter, the vehicle body cannot be driven backward with the working implement in operation. That is, the check function of the check function circuit is reinstated by a deliberate operation to disengage the clutch mechanism while the check function is canceled. This is rational from the operational point of view.
In another preferred embodiment of this invention, the interlock circuit further comprises an indicator lamp unit tuned off when the check function is in operation, and lit or blinked when the check function is canceled by the release function circuit. In this construction, the indicator lamp is lit or blinked only when the check function is off. The operator can readily recognize that a backward operational run is possible.
As further preferred embodiment, the interlock circuit may further comprise a prohibition circuit unit for prohibiting the release function circuit from canceling the check function. Since the cancellation of the check function by the release function circuit can be prohibited, as necessary, the release switch may be made ineffective to permit a backward operational run.
Other features and advantages of this invention will be apparent from the following description of the embodiment to be taken with reference to the drawings.